So as the title says, my idea is for an "inactive" anomaly that causes minor climate change (like, the weather changes in its containment cell, and nowhere else minor). But the kicker would be that this artifact is missing a piece, that based upon inscriptions/lost documents, is theorised to fully activate it and cause much more extensive weather effects over a wider area.

Had the idea after learning about the Liangzhu culture and how it vanished due to severe flood events, perhaps due to being attacked by an anomalous rival tribe? I still need to flesh this out properly, wondering if anyone had any ideas about things that could extend this!

I think it would be stronger if instead of its area of effect being faulty, its overall functionality being faulty.

Like, if you ask the object to produce rain, instead of raining water it rains frogs, or cats and dogs. Then you could give the object a long history of being passed around from culture to culture, with tales like the plagues of Egypt and phrases like "raining cats and dogs" possibly originating from the effects of this object.

That's a good idea, adds a little bit of variety rather than it being some kind of simple anomalous weapon, as well as making a little bit more of a mythos! Guess I just have to find a way to carry that out subtly enough with hints and little bits of history here and there